Rieju 125 SMX [2005-2008]: A Supermoto For the Streets and Beyond

Introduction

The Rieju 125 SMX, produced between 2005 and 2008, is a Spanish-built Supermoto that blends urban agility with off-road curiosity. Built around Yamaha’s reliable 125cc four-stroke engine, this lightweight machine became a favorite for riders seeking a budget-friendly entry into the world of spirited street riding and occasional dirt adventures. With its punchy engine, minimalist design, and adaptable chassis, the SMX 125 carved a niche in the 125cc segment during its era. But how does it hold up today? Let’s throttle into the details.

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Design & Ergonomics: Raw, Functional, and Unapologetically Simple

The Rieju 125 SMX screams “Supermoto” from every angle. Its compact, no-nonsense design features a high-mounted front fender, slim bodywork, and an aggressively styled fuel tank that narrows at the knees for easy grip during hard cornering. Color options ranged from bold red and blue to stealthy black and grey, with later models adding white/blue and black/red schemes. The bike’s aesthetic is industrial yet purposeful—a reminder that this machine was built to be ridden, not polished.

Ergonomics are a mixed bag, typical of the Supermoto genre. The seat height hovers around 900 mm (35.4 inches), which might intimidate shorter riders but feels natural for stand-up riding on uneven terrain. The narrow seat itself is firm—ideal for quick weight shifts but punishing on long hauls. The upright riding position, with wide handlebars and mid-set footpegs, provides excellent control for flicking through traffic or tackling dirt paths. At 107–108 kg (236–238 lbs), the SMX feels almost playful when lifted off the side stand, making it a great choice for new riders or those prioritizing maneuverability.

Fuel capacity varies slightly between models: 7.4–10 liters (1.96–2.64 US gallons). The smaller tank on SMX variants emphasizes its urban focus, while MRX off-road models trade capacity for weight savings.

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Engine & Performance: Yamaha’s Trusty Heart

At the core of the Rieju 125 SMX lies a Yamaha-derived, air-cooled, single-cylinder four-stroke engine. Displacing 124–125cc (7.57–7.63 cubic inches), this powerplant churns out 14.5 HP (10.6 kW)—a figure that keeps it A2 license-friendly in Europe. While these numbers won’t set records, the engine’s broad torque curve and linear power delivery make it surprisingly versatile.

Throttle response is crisp, thanks to the Mikuni VM20SS carburetor. Cold starts can be finicky (a common carbureted bike trait), but the dual electric/kick starter ensures you’re never stranded. The 5-speed gearbox shifts with a satisfying mechanical click, though finding neutral at a stoplight often requires patience. Top speed sits around 100–105 km/h (62–65 mph), with vibrations becoming noticeable above 80 km/h (50 mph). This isn’t a highway cruiser, but it’s a blast on twisty backroads or city streets where its lightweight shines.

Air cooling keeps the design simple, but riders in hot climates or stop-and-go traffic should monitor temps. Aftermarket oil coolers (available at MOTOPARTS.store) can add peace of mind for extended rides.

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Handling & Suspension: Where the SMX Earns Its Stripes

The Rieju’s high-resistance steel perimeter frame strikes a balance between rigidity and flex, offering precise feedback when cornering. SMX models roll on 17-inch front and rear wheels shod with street-biased tires (100/80-17 front, 120–130/80-17 rear), while MRX enduro variants swap to a 21-inch front wheel (90/90-21) for off-road prowess. The SMX’s setup leans heavily into its Supermoto DNA—expect knee-down potential on smooth tarmac and enough grip for gravel detours.

Suspension components vary by year and model. Earlier SMX bikes feature 35mm upside-down forks and a monoshock rear, while later iterations upgrade to Paioli or Marzocchi units with adjustable preload. Travel is generous for a 125cc bike: ~200 mm (7.9 inches) at the front and rear. The setup soaks up potholes and curbs with ease, though aggressive riders might crave more damping control for track use.

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Braking System: Adequate, But Begging for Upgrades

Braking duties are handled by a 220mm front disc (early models) or 200mm disc (later years) with a dual-piston caliper, paired with a 200mm rear disc. Stopping power is sufficient for the bike’s weight, but the initial bite lacks aggression. Swapping to sintered pads (available in our store) sharpens response, while braided steel lines reduce squishiness under hard braking.

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Competition: How the SMX Stacks Up

The 125cc Supermoto segment in the mid-2000s was fiercely competitive. Here’s how the Rieju held its ground:

• Aprilia SX 125: Aprilia’s two-stroke rival packed more punch (25+ HP) but demanded frequent rebuilds. The SMX’s four-stroke engine appealed to riders prioritizing reliability over peak power.
• Yamaha WR125X: Sharing the same engine as the SMX, the WR125X boasted Yamaha’s build quality but came at a higher price. The Rieju undercut it with comparable performance and a rawer, more customizable platform.
• Honda CRF125: Honda’s offering leaned harder into off-road capability but felt cumbersome on pavement. The SMX struck a better balance for urban riders.

The Rieju’s ace? Its Yamaha engine reliability paired with Spanish chassis flair. While not the fastest, it’s a forgiving platform for honing riding skills.

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Maintenance: Keeping Your SMX Alive and Thriving

The Rieju 125 SMX is a mechanic’s dream—simple, accessible, and free of modern electronics. Key maintenance tips:

1. Carburetor Care: The Mikuni VM20SS is robust but sensitive to stale fuel. Clean jets annually and consider a rebuild kit (available at MOTOPARTS.store) if idle becomes erratic.
2. Chain & Sprockets: The O-ring chain lasts 15,000–20,000 km (9,300–12,400 miles) with regular lubrication. Swap to a DID chain for longevity.
3. Oil Changes: Use 10W-40 JASO MA2 oil every 3,000 km (1,860 miles). The engine’s separate lubrication system (on later models) simplifies this process.
4. Valve Adjustments: Check every 6,000 km (3,730 miles). Shim-under-bucket design requires precision but ensures long-term reliability.
5. Suspension Tuning: Stiffer springs improve road manners for heavier riders. Upgrade to progressive-rate springs for off-road use.

Common upgrades include:
- High-flow air filters
- Aftermarket exhausts (for weight savings, not power gains)
- LED lighting kits for visibility

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Conclusion: A Timeless Playmate

The Rieju 125 SMX isn’t about brute force or cutting-edge tech—it’s about the joy of riding. Whether slicing through city traffic, scraping pegs on mountain passes, or exploring fire roads, this bike reminds you why lightweight, simple motorcycles are so addictive. Its Yamaha heart ensures parts remain plentiful, and its minimalist design invites customization.

For riders seeking an affordable, reliable entry into Supermoto culture—or veterans craving a back-to-basics thrill—the SMX 125 remains a compelling choice. And when it’s time to tweak, tune, or rebuild, MOTOPARTS.store has the gear to make it yours.

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Specifications sheet

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